Wearable device with multibiometry

ABSTRACT

It is provided a wearable device for determining when a user has fallen down. The wearable device comprises: a first biometric sensor for obtaining first biometric data of the user, wherein the first biometric sensor is a first accelerometer configured to measure acceleration of a part of a first limb of the user; a second biometric sensor for obtaining second biometric data of the user comprising a finger pressure parameter; and a third biometric sensor for obtaining third biometric data, the third biometric sensor being a second accelerometer configured to measure acceleration of a body part of the user being distinct from the first limb. The wearable device is configured to determine an identity of the user is based on the first biometric data, the second biometric data and the third biometric data, the identity being used to control access to a physical space, and to determine when the user has fallen down.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Pat. Application No.17/510,129, filed Oct. 25, 2021, which is a continuation of U.S. Pat.Application No. 16/756,747, filed Apr. 16, 2020, now U.S. Pat. No.11,189,149, issued Nov. 30, 2021, which is a national stage applicationunder 35 U.S.C. 371 and claims the benefit of PCT Application No.PCT/EP2018/078967 having an international filing date of Oct. 23, 2018,which designated the United States, which PCT application claimed thebenefit of European Patent Application No. 17198077.4 filed Oct. 24,2017, the disclosure of each of which are incorporated herein byreference.

TECHNICAL FIELD

The invention relates to identification of a user using a wearabledevice.

BACKGROUND

With online shopping steadily increasing, deliveries of physical goodsare also increasing. Consumers want fast and cheap delivery, and thedelivery companies want efficiency and safety for their deliveries.However, thefts from delivery vehicles and attacks against drivers areincreasing since the value of the goods increases.

Current security solutions for delivery vehicles rely on traditionalvehicle locks or even padlocks. Moreover, there are no satisfactorysecurity solutions for drivers of delivery vehicles.

SUMMARY

It is an object to improve security for drivers of cargo vehicles.

According to a first aspect, it is provided a wearable device fordetermining when a user has fallen down. The wearable device comprises:a first biometric sensor for obtaining first biometric data of the user,wherein the first biometric sensor is a first accelerometer configuredto measure acceleration of a part of a first limb of the user; a secondbiometric sensor for obtaining second biometric data of the usercomprising a finger pressure parameter; and a third biometric sensor forobtaining third biometric data, the third biometric sensor being asecond accelerometer configured to measure acceleration of a body partof the user being distinct from the first limb of the user. The wearabledevice is configured to determine an identity of the user is based onthe first biometric data, the second biometric data and the thirdbiometric data, the identity being used to control access to a physicalspace, and to determine when the user has fallen down based on the firstbiometric data and the third biometric data.

The first biometric sensor may comprise a fingerprint sensor.

The first biometric sensor may comprise a blood flow sensor.

The first biometric sensor may comprise a gyro.

The physical space may form part of a vehicle.

According to a second aspect, it is provided a method for determiningwhen a user has fallen down. The method is performed in a wearabledevice and comprising the steps of: obtaining first biometric data ofthe user using a first biometric sensor of the wearable device, whereinthe first biometric sensor is a first accelerometer configured tomeasure acceleration of a part of a first limb of the user; obtainingsecond biometric data of the user using a second biometric sensor of thewearable device, the second biometric data comprising a finger pressureparameter; obtaining third biometric data of the user using a thirdbiometric sensor of the wearable device, wherein the third biometricsensor is a second accelerometer configured to measure acceleration of abody part of the user being distinct from the first limb of the user;determining an identity of the user based on the first biometric dataand the second biometric data; and determining when the user has fallendown based on the first biometric data and the third biometric data.

According to a third aspect, it is provided a computer program fordetermining when a user has fallen down. The computer program comprisingcomputer program code which, when run on a wearable device causes thewearable device to: obtain first biometric data using a first biometricsensor of the wearable device, wherein the first biometric sensor is afirst accelerometer configured to measure acceleration of a part of afirst limb of the user; obtain second biometric data using a secondbiometric sensor of the wearable device, the second biometric datacomprising a finger pressure parameter; obtain third biometric data ofthe user using a third biometric sensor of the wearable device, whereinthe third biometric sensor is a second accelerometer configured tomeasure acceleration of a body part of the user being distinct from thefirst limb of the user; determine an identity of the user based on thefirst biometric data and the second biometric data and determine whenthe user has fallen down based on the first biometric data and the thirdbiometric data.

According to a fourth aspect, it is provided a computer program productcomprising a computer program according to the third aspect and acomputer readable means on which the computer program is stored.

Generally, all terms used in the claims are to be interpreted accordingto their ordinary meaning in the technical field, unless explicitlydefined otherwise herein. All references to “a/an/the element,apparatus, component, means, step, etc.” are to be interpreted openly asreferring to at least one instance of the element, apparatus, component,means, step, etc., unless explicitly stated otherwise. The steps of anymethod disclosed herein do not have to be performed in the exact orderdisclosed, unless explicitly stated.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now described, by way of example, with reference to theaccompanying drawings, in which:

FIG. 1 is a schematic diagram illustrating an environment in whichembodiments presented herein can be applied;

FIG. 2 is a schematic diagram illustrating an embodiment of a wearabledevice of FIG. 1 ;

FIG. 3 is a schematic diagram illustrating an embodiment of a wearabledevice of FIG. 1 implemented using several sections;

FIG. 4 is a schematic diagram illustrating components of the wearabledevice of FIG. 1 ;

FIG. 5 is a flow chart illustrating a method for determining when a userhas fallen down, performed in the wearable device of FIG. 1 ; and

FIG. 6 shows one example of a computer program product comprisingcomputer readable means.

DETAILED DESCRIPTION

The invention will now be described more fully hereinafter withreference to the accompanying drawings, in which certain embodiments ofthe invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided byway of example so that this disclosure will be thorough and complete,and will fully convey the scope of the invention to those skilled in theart. Like numbers refer to like elements throughout the description.

FIG. 1 is a schematic diagram illustrating an environment in whichembodiments presented herein can be applied.

A user 1 is a logistics person associated with a vehicle 20, forinstance the currently assigned driver of the vehicle. The vehicle 20 issuitable for carrying cargo and can be a van, a lorry, a car, etc. Thecargo can be loaded in the vehicle 20 e.g. in the form of boxes,optionally on pallets. The vehicle 20 is provided with a back door 21 aand one or more cabin doors 21 c (only one seen in FIG. 1 ). Thefunction of the back door 21 a can equally well be performed by a taillift and/or roller shutter. Optionally, a side door 21 b for access tothe cargo area of the vehicle is provided. The back door 21 a is securedby a first electronic lock 22 a, the cabin door(s) 21 c are secured by athird electronic lock 22 c and the optional side door 21 b is secured byan optional second electronic lock 22 b. Optionally, an electronicaccess control device 23 controls access to operation of the vehicle,corresponding to an ignition key.

The user 1 carries a wearable device 2. A wearable device is anelectronic device which can be worn by the user. For instance thewearable device can be in the form of a wristband or watch. As explainedin more detail below, the wearable device 2 is used to identify the user1 using at least two biometric sensors.

The user 1 can request access to a physical space by placing thewearable device 2 in close proximity (e.g. centimetres) or in contactwith a tag (not shown) associated with the electronic lock securing thephysical space in question. The communication between the tag and thewearable device 2 can e.g. be based on RFID (Radio FrequencyIdentification) or NFC (Near Field Communication). This will trigger theelectronic lock to perform an access control procedure for the useridentified by the wearable device 2. If the access control procedure ispositive, the electronic lock will be set in an unlocked state, allowingthe user to access the physical space. The same procedure can be used toset the electronic lock in a locked state.

An access manager 7 is a computer which is used to allocate access tothe user 1 as needed, to be able to open the electronic locks 22 a-c.The wearable device 2 can communicate with the access manager, e.g.using a cellular network module within the wearable device 2 or via asmartphone connected with the wearable device 2 over a short rangewireless link.

A usage scenario in the environment illustrated in FIG. 1 will now bedescribed.

At the start of a shift, the user 1 reports to a logistics centre, atwhich the user is assigned a vehicle and a delivery schedule for theday. The user accepts by identifying him/herself using the wearabledevice.

Optionally, the vehicle can be started only after the user has providedidentification on the wearable device.

Once the user arrives at a delivery location, the user exits the cabinand walks around to the back of the vehicle. The lock of the back dooris opened by the user providing identification on the wearable device.Once the user has picked up the item to be delivered, e.g. a parcel, theuser exits the vehicle and locks the back door by identifying using thewearable device. Alternatively, an accelerometer in the vehicle is usedto detect when the user has exited the vehicle, at which point the backdoor is locked. This detection can be based on an absence of movement orbased on movement which differs from a movement pattern of the user. Themovement pattern of the user has in that case been calibrated inadvance, by the user moving about the cargo space in the vehicle for 3-6minutes when in a calibration mode.

Alternatively, the back door is locked every time it is closed.

The wearable device can be used to improve security for the user. Forinstance, if the user is attacked and is forced on the ground, one ormore accelerometers (see below) can detect this and send an alarm to acentral office. Analogously, the wearable device can detect if the userfalls down and does not get up again, e.g. for a health reason, at whichpoint the wearable device sends an alarm.

Additional logic can be applied to enhance security. For instance, thewearable device may poll to require identification at regular intervalsto indicate that the user is safe. This can be prompted by a smallvibration of the wearable device which is only sensed by the user.Hence, every so often, the wearable device vibrates and the userprovided identification, which is interpreted as the user being safe. Ifthe user is kidnapped or under threat, the user can abstain fromproviding identification when prompted, which then triggers an alarm tobe sent from the wearable device. The hours during which the polling ofidentification occurs can be based on working hours or awake hours.

If the user locks the back door using the wearable device, the cabindoors can be locked automatically.

FIG. 2 is a schematic diagram illustrating an embodiment of a wearabledevice 2 of FIG. 1 in the form of a wristband. The wearable device 2comprises a first biometric sensor 3 a for obtaining first biometricdata and a second biometric sensor 3 b for obtaining second biometricdata. The second biometric sensor 3 b captures second biometric datacomprising a finger pressure parameter.

The wearable device 2 is configured to determine an identity of the user1 based on the first biometric data and the second biometric data.

By measuring the finger pressure, an additional biometric parameter iscaptured which is difficult to copy and easy for the user to remember.The finger pressure parameter can be a curve of how the finger pressurevaries over time, which improves the accuracy of identifying the user.The specific finger pressure pattern for the user needs to be capturedinitially, and may need to be periodically calibrated over time.

In this embodiment, the wearable device 2 is in the form of a wristband,to be worn around the wrist of the user.

The first biometric sensor 3 a can comprise a fingerprint sensor. Thisallows for convenient identification of the user, e.g. by comparing acaptured fingerprint with one or more templates. Optionally, the firstbiometric sensor 3 a comprises a blood flow sensor. The blood flowsensor captures the blood flow, which varies over time in a userspecific manner. Hence, the blood flow over time can be compared withblood flow templates to determine an identity of the user. Since thefirst biometric sensor 3 a is used for finger pressure detection, theuser needs to press the wearable device towards the body. This increasesthe quality of blood flow capturing. Optionally, the first biometricsensor 3 a comprises a voice recognition unit. The spoken voice of auser is then captured using a microphone. The captured voice can becompared with voice templates to determine an identity of the user.

Optionally, the first biometric sensor 3 a comprises an iris recognitionunit. The iris of a user is then captured using a camera. The capturediris can be compared with iris templates to determine an identity of theuser. The iris recognition unit can form part of the wearable device, ora rear vision camera of the vehicle can be used for this biometricsensor.

Optionally, the first biometric sensor 3 a comprises a face recognitionunit. The face of a user is then captured using a camera. The capturedface can be compared with face templates to determine an identity of theuser. The face recognition unit can form part of the wearable device, ora rear vision camera of the vehicle can be used for this biometricsensor.

The first biometric sensor 3 a comprises an accelerometer, optionallycombined with a gyro. The movement pattern of a user is then capturedusing the accelerometer and optionally the gyro. The captured movementpatter can be compared with movement templates to determine an identityof the user.

Optionally, the first biometric sensor 3 a comprises a breathalyser.Presence and/or extent of components of expired air of a user is thencaptured. The captured presence and/or extent of components can becompared with templates to determine an identity of the user.

Hence, the first biometric sensor 3 a can comprise any suitable sensorfor sensing a biometric of the user. Additional biometric sensors can beadded to further improve accuracy of user identifications. More sensorsimply reduces risk of false positive and false negative identifications.

Optionally, there is a sensor which detects if the wearable device 2 isremoved from a users. This enables even greater reliability indetermining which user carries the wearable device 2.

FIG. 3 is a schematic diagram illustrating an embodiment of a wearabledevice 2 of FIG. 1 implemented using several sections 2 a and 2 b. Inthis embodiment, the wearable device 2 is made up by two separatesections, a first section 2 a and a second section 2 b. The sections 2a, 2 b are separate but can communicate with each other using a wirelesslink, e.g. Bluetooth Low Energy (BLE), Bluetooth, etc.

The first section 2 a can be in the form of the wristband of FIG. 2 .The first section is attached to a limb 10 of the user, in this examplean arm. The second section 2 b can be attached to a body part of theuser being distinct from the first limb 10 of the user. For instance,the second section 2 b can be attached to a belt (and thus the torso ofthe user 1), a hat of the user, a shoe of the user, an ear of the user(as an ear clip), etc.

The second section 2 b comprises a third biometric sensor 3 c forobtaining third biometric data, wherein the wearable device 2 isconfigured to determine the identity of the user 1 based also on thethird biometric data. When the first biometric 3 a sensor is a firstaccelerometer, the third biometric sensor 3 b can be a secondaccelerometer. Hence, the first accelerometer can be configured tomeasure acceleration of a part of a first limb 10 of the user 1 and thesecond accelerometer can be configured to measure acceleration ofanother body part of the user 1. The accelerometers can be triaxleaccelerometers and optionally comprises respective gyros.

By using two separate accelerometers on separate body parts of the user,the state of the user can be determined which much greater reliability.For instance, the respective accelerations can be double integrated toobtain a shift in position, which can e.g. be used to detect when theuser 1 has fallen down or is otherwise in a horizontal position. Inother words, by using multiple accelerometers on different body parts ofthe user, the wearable can detect movement with great accuracy andreliability. The detection of when a user has fallen down can also bemade based on fast Fourier transform (FFT) of the acceleration signalsfrom the two accelerometers and comparing with threshold values in oneor more frequency components obtained through the FFT. When present, thegyro can also be of great help to identify the position of the user 1.

FIG. 4 is a schematic diagram illustrating components of the wearabledevice 2 of FIG. 1 . A processor 60 is provided using any combination ofone or more of a suitable central processing unit (CPU), multiprocessor,microcontroller, digital signal processor (DSP), application specificintegrated circuit etc., capable of executing software instructions 67stored in a memory 64, which can thus be a computer program product. Theprocessor 60 can be configured to execute the method described withreference to FIG. 5 below.

The memory 64 can be any combination of random access memory (RAM) andread only memory (ROM). The memory 64 also comprises persistent storage,which, for example, can be any single one or combination of magneticmemory, optical memory, solid-state memory, or even remotely mountedmemory.

A data memory 66 is also provided for reading and/or storing data duringexecution of software instructions in the processor 60. The data memory66 can be any combination of random access memory (RAM) and read onlymemory (ROM). The data memory 66 can e.g. comprise templates forbiometric identification of a user.

The wearable device 2 further comprises an I/O interface 62 forcommunicating with other external entities. Optionally, the I/Ointerface 62 also includes a user interface.

A transceiver of the I/O interface 62 comprises suitable analogue anddigital components to allow signal transmission and signal receptionwith a wireless device using one or more antennas. The transceiver caninclude a cellular module (using e.g. LTE (Long Term Evolution) orW-CDMA (wideband code division multiple access) for data access to theInternet.

Alternatively or additionally, the transceiver comprises a short-rangecommunication module, e.g. BLE or Bluetooth for communication with asmartphone, to thereby gain data access to the Internet.

In FIG. 4 , a first biometric sensor 3 a, a second biometric sensor 3 band a third biometric sensor 3 c are shown. Additional biometric sensorscan be added to increase reliability of biometric identification of auser.

Other components of the wearable device 2 are omitted in order not toobscure the concepts presented herein.

It is to be noted that the wearable device 2 can be provided in two ormore sections (see e.g. FIG. 3 ), in which case the different sectionsof the wearable device 2 can communicate with each other using awireless link, e.g. BLE.

FIG. 5 is a flow chart illustrating a method for determining when a userhas fallen down, performed in the wearable device of FIG. 1 .

In an obtain first biometric data step 40, the wearable device obtainsfirst biometric data of the user using a first biometric sensor of thewearable device. The first biometric sensor is a first accelerometerconfigured to measure acceleration of a part of a first limb of theuser. Hence, the first biometric data is based on the acceleration ofthe first biometric sensor. In one embodiment, the first biometric datais the measured acceleration of the first biometric sensor.

In an obtain second biometric data step 42, the wearable device obtainssecond biometric data of the user using a second biometric sensor of thewearable device, the second biometric data comprising a finger pressureparameter.

In an obtain third biometric data step 43, the wearable device obtainsthird biometric data of the user using a third biometric sensor of thewearable device The third biometric sensor is a second accelerometerconfigured to measure acceleration of a body part of the user beingdistinct from the first limb of the user. Hence, the third biometricdata is based on the acceleration of the third biometric sensor. In oneembodiment, the third biometric data is the measured acceleration of thethird biometric sensor.

In a determine identity step 44, the wearable device determines anidentity of the user based on the first biometric data and the secondbiometric data. The identity is used to control access to a physicalspace, e.g. of the vehicle.

In a determine when fallen down step 45, the wearable device determineswhen the user has fallen down based on the first biometric data and thethird biometric data.

The determining of when the user has fallen down can be based on doubleintegrating acceleration data to determine a vertical movementdifference between the first biometric sensor and the third biometricsensor. This is particularly useful when the vertical position differssignificantly when standing up, e.g. if the first biometric sensor is ona wrist and the third biometric sensor is in a necklace. When the userhas fallen down, the vertical position difference is much less than whenthe user is standing up.

The determining of when the user has fallen down can be based onperforming a fast Fourier transform (FFT) of the accelerations detectedby the first biometric sensor and the third biometric sensor. When auser falls down, the frequency components of the acceleration issignificantly different from a deliberate motion, e.g. lying down on asofa. This is exploited using the FFT processing.

The determining of when the user has fallen down is of great importancefor the security of the user. The central control centre alerted of thefallen down user, allowing actions to be performed to ensure thesecurity of the user. Additionally, when potential attackers learn thatthe fallen down detection is used, they will be less prone to followthrough with plans to attack users. Using multiple biometric sensor todetermine identity of the user gives an identification which isvirtually impossible to spoof by an attacker. Moreover, there is atraceability on individual level, rather than based on a physicalcredential item such as a key card, fob, etc. The traceability onindividual level provides a greater security and the recipient can trustthe driver to a greater extent. In this way, drivers that may have hadto wait for a specific person to receive the delivery may be givenaccess to a building to drop off the delivery directly, making thedelivery more efficient and thus saving time and cost.

FIG. 6 shows one example of a computer program product comprisingcomputer readable means. On this computer readable means, a computerprogram 91 can be stored, which computer program can cause a processorto execute a method according to embodiments described herein. In thisexample, the computer program product is an optical disc, such as a CD(compact disc) or a DVD (digital versatile disc) or a Blu-Ray disc. Asexplained above, the computer program product could also be embodied ina memory of a device, such as the computer program product 64 of FIG. 4. While the computer program 91 is here schematically shown as a trackon the depicted optical disk, the computer program can be stored in anyway which is suitable for the computer program product, such as aremovable solid state memory, e.g. a Universal Serial Bus (USB) drive.

Here now follows a list of embodiments from another perspective,enumerated with roman numerals.

-   i. A wearable device for identifying a user, the wearable device    comprising:    -   a first biometric sensor for obtaining first biometric data of        the user; and    -   a second biometric sensor for obtaining second biometric data of        the user comprising a finger pressure parameter;    -   wherein the wearable device is configured to determine an        identity of the user is based on the first biometric data and        the second biometric data, the identity being used to control        access to a physical space.-   ii. The wearable device according to embodiment i, wherein the first    biometric sensor is a fingerprint sensor.-   iii. The wearable device according to embodiment i, wherein the    first biometric sensor is a blood flow sensor.-   iv. The wearable device according to embodiment i or ii, further    comprising a third biometric sensor for obtaining third biometric    data, wherein the wearable device is configured to determine the    identity of the user based also on the third biometric data.-   v. The wearable device according to embodiment iv, wherein the first    biometric sensor is a first accelerometer and the third biometric    sensor is a second accelerometer.-   vi. The wearable device according to embodiment v, wherein the first    accelerometer is configured to measure acceleration of a part of a    first limb of the user and the second accelerometer is configured to    measure acceleration of a body part of the user being distinct from    the first limb of the user.-   vii. The wearable device according to any one of the preceding    embodiments, wherein the first biometric sensor comprises a gyro.-   viii. The wearable device according to any one of the preceding    embodiments, wherein the physical space forms part of a vehicle.-   ix. A method for identifying a user, the method being performed in a    wearable device and comprising the steps of:    -   obtaining first biometric data of the user using a first        biometric sensor of the wearable device;    -   obtaining second biometric data of the user using a second        biometric sensor of the wearable device, the second biometric        data comprising a finger pressure parameter; and    -   determining an identity of the user based on the first biometric        data and the second biometric data.-   x. A computer program for identifying a user, the computer program    comprising computer program code which, when run on a wearable    device causes the wearable device to:    -   obtain first biometric data using a first biometric sensor of        the wearable device;    -   obtain second biometric data using a second biometric sensor of        the wearable device, the second biometric data comprising a        finger pressure parameter; and    -   determine an identity of the user based on the first biometric        data and the second biometric data.-   xi. A computer program product comprising a computer program    according to embodiment x and a computer readable means on which the    computer program is stored.

The invention has mainly been described above with reference to a fewembodiments. However, as is readily appreciated by a person skilled inthe art, other embodiments than the ones disclosed above are equallypossible within the scope of the invention, as defined by the appendedpatent claims.

1. A wearable device for determining when a user has fallen down, thewearable device comprising: a first biometric sensor for obtaining firstbiometric data of the user, wherein the first biometric sensor is afirst accelerometer configured to measure acceleration of a part of afirst limb of the user; and an auxiliary biometric sensor for obtainingauxiliary biometric data, the auxiliary biometric sensor being a secondaccelerometer configured to measure acceleration of a body part of theuser being distinct from the first limb of the user; a processor; and amemory storing instructions that, when executed by the processor, causethe wearable device to: determine when the user has fallen down based onthe first biometric data and the auxiliary biometric data.
 2. Thewearable device according to claim 1, wherein the first biometric sensorcomprises a fingerprint sensor.
 3. The wearable device according toclaim 1, wherein the first biometric sensor comprises a blood flowsensor.
 4. The wearable device according to claim 1, wherein theinstructions to determine when the user has fallen down comprisesinstructions that, when executed by the processor, cause the wearabledevice to: determine when the user has fallen down based on doubleintegrating acceleration data to determine a vertical movementdifference between the first biometric sensor and the auxiliarybiometric sensor.
 5. The wearable device according to claim 1, whereinthe instructions to determine when the user has fallen down comprisesinstructions that, when executed by the processor, cause the wearabledevice to: determine when the user has fallen down based on performing afast Fourier transform of the accelerations detected by the firstbiometric sensor and the auxiliary biometric sensor.
 6. The wearabledevice according to claim 1, wherein the first biometric sensorcomprises a gyro.
 7. The wearable device according to claim 1, whereinthe physical space forms part of a vehicle.
 8. The wearable deviceaccording to claim 1, further comprising instructions that, whenexecuted by the processor, cause the wearable device to: send an alarmindicating that the user has fallen down.
 9. A method for determiningwhen a user has fallen down, the method being performed in a wearabledevice and comprising: obtaining first biometric data of the user usinga first biometric sensor of the wearable device, wherein the firstbiometric sensor is a first accelerometer configured to measureacceleration of a part of a first limb of the user; obtaining auxiliarybiometric data of the user using an auxiliary biometric sensor of thewearable device, wherein the auxiliary biometric sensor is a secondaccelerometer configured to measure acceleration of a body part of theuser being distinct from the first limb of the user; and determiningwhen the user has fallen down based on the first biometric data and theauxiliary biometric data.
 10. The method according to claim 9, whereinthe determining when the user has fallen down comprises determining whenthe user has fallen down based on double integrating acceleration datato determine a vertical movement difference between the first biometricsensor and the auxiliary biometric sensor.
 11. The method according toclaim 9, wherein the determining when the user has fallen down comprisesdetermining when the user has fallen down based on performing a fastFourier transform of the accelerations detected by the first biometricsensor and the auxiliary biometric sensor.
 12. The method according toclaim 9, further comprising: sending an alarm indicating that the userhas fallen down.
 13. A computer program for determining when a user hasfallen down, the computer program comprising computer program codewhich, when run on a wearable device causes the wearable device to:obtain first biometric data using a first biometric sensor of thewearable device, wherein the first biometric sensor is a firstaccelerometer configured to measure acceleration of a part of a firstlimb of the user; obtain auxiliary biometric data of the user using anauxiliary biometric sensor of the wearable device, wherein the auxiliarybiometric sensor is a second accelerometer configured to measureacceleration of a body part of the user being distinct from the firstlimb of the user; and determine when the user has fallen down based onthe first biometric data and the auxiliary biometric data.
 14. Acomputer program product comprising a computer program according toclaim 13 and a computer readable means on which the computer program isstored.